Conventionally, various puncturing devices to sample blood from skin of human and animals have been invented for blood analysis, and in recent years, a puncturing device has been invented that accumulates biasing force for puncturing at the same time as a puncturing needle is mounted in the puncturing device (see, for example, Patent Literature 1). This puncturing device performs operation including puncturing and removing, by means of two compression springs, that is, a first compression spring for puncturing and a second compression spring for removing. In addition, a puncturing needle has been developed, in which the part having contacted skin is entirely discarded in order to prevent infection due to adhesion of blood.
Patent Literature 2 discloses a puncturing device including a first biasing means for biasing a puncturing plunger toward the tip and a sucking plunger that has an airtight sealing member and reduces pressure in a housing by moving toward the base end.
Patent literature 3 discloses an apparatus that samples blood from patients in a painless manner, in order to monitor glucose.
FIG. 1 shows a decompression and blood sampling mechanism by means of a spring, used in a conventional puncturing device.
As shown in FIG. 1, decompression and blood sampling mechanism 1 is configured to include piston 2, cylinder 3 that slidably accommodates piston 2, spring 4 that biases to push piston 2 outward, and packing 5 mounted on the outer surface of end part 2a of piston 2.
Packing 5 keeps sealed space 7 airtight, which is formed by bottom surface 2b of end part 2a of piston 2, inner surface 3a of cylinder 3 and skin 6 contacting.
FIG. 1 shows a usual state in which puncturing operation is not performed with the above-described configuration. Now, decompression operation in a puncturing device using decompression and blood sampling mechanism 1 will be described.
First, as shown in FIG. 1B, while spring 4 is compressed in advance, skin 6 contacts inner surface 3a of cylinder 3 to create sealed space 7.
Next, as shown in FIG. 1C, pressing piston 2 is stopped. Then, compressed spring 4 returns to the original state to increase the volume of sealed space 7. By this means, the pressure in sealed space 7 reduces and skin 6 is lifted up, and therefore blood is easily sampled by a puncturing device (not shown) from lifted skin 6.
Next, as shown in FIG. 1D, piston 2 is pressed again to adjust the pressure to the atmospheric pressure, and then skin 6 is removed.
Here, in a case in which the operation shown in FIG. 1D is not performed, when skin 6 is removed when blood is sampled (reduced pressure state: see FIG. 1C), the air rapidly flows in and therefore blood scatters in the puncturing device.
In order to prevent this state, it is necessary to push piston 2 into cylinder 3 again after blood is sampled, as shown in FIG. 1D.
FIG. 2 is a perspective view showing the blood sampling apparatus disclosed in Patent Literature 3. In FIG. 2, the housing of the apparatus is open.
As shown in FIG. 2, blood drawing device 1100 has housing 1102, and housing 1102 has receiving part 1102a and projecting part 1102b. Gasket 1104 seals between receiving part 1102a and projecting part 1102b in housing 1102 and separates receiving part 1102a from projecting part 1102b. Projecting part 1102b is tightly fitted into receiving part 1102a by friction. Projecting elements 1102c and 1102d are used to guide projecting part 1102b to receiving part 1102a. A vacuum pump (not shown), incising assembly 1108, a buttery (not shown) and an electronic device (not shown) are provided in housing 1102. Switch 1109 is provided to activate the electronic device.
During blood sampling, projecting part 1102b is tightly fitted into receiving part 1102a. Receiving part 1102a to contact skin is provided with seal 1110, in housing 1102 of device 1100. Opening 1112 in receiving part 1102a is surrounded by seal 1110. A blood drawing chamber nearby glucose detector 1114 communicates with the surface of skin through opening 1112 in receiving part 1102a. Device 1100 is placed on a region on the surface of skin from which incising assembly 1108 samples blood. In order to sample blood, receiving part 1102a in hosing 1102 of device 1100 is put on skin, and a vacuum is created using seal 1110.
The vacuum pump is operated by pressing switch 1109 to produce sucking action. Skin surrounded by seal 1110 is engorged with blood by sucking action of the vacuum pump. By stretching and lifting skin up to opening 1112, the skin is engorged with blood. After an appropriate period of time usually preset by a programmer who programs electronic devices has passed, incising assembly 1108 is launched to make lancet 1116 penetrate skin which has been lifted up to opening 1112 and engorged with blood. It is preferred to automatically launch lancet 1116 using a solenoid valve (not shown) with a vacuum piston (not shown).
Glucose detector 1114 is inserted in slot 1118 in projecting part 1102b in housing 1102. Receiving part 1102a in housing 1102 moves glucose detector 1114 to a position suitable for testing. The result obtained from glucose detector 1114 is displayed on screen 1120. Receiving part 1102a is separated from projecting part 1102b when lancet 1116 or glucose detector 1114 is replaced. In the process of blood sampling, projecting part 1102b is tightly fitted into receiving section 1102a. 
As described above, in device 1100, a sensor (glucose detector 1114) is provided in space in which pressure is reduced. In order to reduce pressure, it is essential that the entire sensor is placed in predetermined space and measured.